Revert "Update to Dom4j 2.1.0"
Revert "Update to Dom4j 2.1.0"

This reverts commit c319c5eaac808fbcba30b8bb24fa00184adb13b4.

Dom4J 2.1.0 uses Java class version 52.0 (ie Java 8):

https://github.com/dom4j/dom4j/commit/9b141527f6715dc2f3462cb6531ed6529a5d3008

As xml-maven-format-plugin aims to support Java 7, we will need to revert.

acegi/xml-format-maven-plugin